diff --git a/src/orcv2.jl b/src/orcv2.jl
index 7434fbaf..5edffe19 100644
--- a/src/orcv2.jl
+++ b/src/orcv2.jl
@@ -176,12 +176,13 @@ function JITDylib(es::ExecutionSession, name; bare=false)
     JITDylib(ref)
 end
 
-@checked struct DefinitionGenerator
+abstract type AbstractDefinitionGenerator end
+@checked struct DefinitionGenerator <: AbstractDefinitionGenerator
     ref::API.LLVMOrcDefinitionGeneratorRef
 end
 Base.unsafe_convert(::Type{API.LLVMOrcDefinitionGeneratorRef}, dg::DefinitionGenerator) = dg.ref
 
-function add!(jd::JITDylib, dg::DefinitionGenerator)
+function add!(jd::JITDylib, dg::AbstractDefinitionGenerator)
     API.LLVMOrcJITDylibAddGenerator(jd, dg)
 end
 
@@ -191,7 +192,82 @@ function CreateDynamicLibrarySearchGeneratorForProcess(prefix)
     DefinitionGenerator(ref[])
 end
 
-# LLVMOrcCreateCustomCAPIDefinitionGenerator(F, Ctx)
+# We can do this async by copying content of `LookupState` and setting it to
+# C_NULL and returning ErrorSuccess. We then would need to call `LookupContinue`
+# but that function was only added in LLVM 15 to the API.
+#
+# Note LookupSet get's destroyed when we return here
+function DefinitionGeneratorTryToGenerateFunction(
+    GeneratorObj::API.LLVMOrcDefinitionGeneratorRef, ctx::Ptr{Cvoid},
+    LookupState::Ptr{API.LLVMOrcLookupStateRef}, Kind::API.LLVMOrcLookupKind,
+    JD::API.LLVMOrcJITDylibRef, JDLookupFlags::API.LLVMOrcJITDylibLookupFlags,
+    LookupSet::API.LLVMOrcCLookupSet, LookupSetSize::Csize_t)::API.LLVMErrorRef
+
+    dg = Base.unsafe_pointer_to_objref(ctx)::CustomDefinitionGenerator
+    @assert dg.dg.ref === GeneratorObj
+    lookupSet = Base.unsafe_wrap(Array, LookupSet, LookupSetSize, own=false)
+    return dg.callback(Kind, JITDylib(JD), JDLookupFlags, lookupSet)::API.LLVMErrorRef
+end
+
+mutable struct CustomDefinitionGenerator <: AbstractDefinitionGenerator
+    callback
+    dg::DefinitionGenerator
+    function CustomDefinitionGenerator(callback)
+        this = new(callback)
+        push!(CUSTOM_DG_ROOTS, this) # Globally root DefinitionGenerator
+
+        ref = API.LLVMOrcCreateCustomCAPIDefinitionGenerator(
+            @cfunction(DefinitionGeneratorTryToGenerateFunction,
+                API.LLVMErrorRef,
+                (API.LLVMOrcDefinitionGeneratorRef, Ptr{Cvoid},
+                 Ptr{API.LLVMOrcLookupStateRef}, API.LLVMOrcLookupKind,
+                 API.LLVMOrcJITDylibRef, API.LLVMOrcJITDylibLookupFlags,
+                 API.LLVMOrcCLookupSet, Csize_t)),
+            Base.pointer_from_objref(this)
+        )
+
+        this.dg = DefinitionGenerator(ref)
+        return this
+    end
+end
+Base.cconvert(::Type{API.LLVMOrcDefinitionGeneratorRef}, dg::CustomDefinitionGenerator) = dg.dg
+
+# todo: Delete
+const CUSTOM_DG_ROOTS = Base.IdSet{CustomDefinitionGenerator}()
+
+function DynamicLibDefinitionGenerator(path)
+    handle = Libdl.dlopen(path)
+
+    function libdl_definitions(kind, JD, lookupFlags, lookupSet)
+        @assert kind == API.LLVMOrcLookupKindStatic
+        @assert lookupFlags == API.LLVMOrcJITDylibLookupFlagsMatchAllSymbols
+
+        symbols = API.LLVMJITCSymbolMapPair[]
+        for lookup in lookupSet
+            if lookup.LookupFlags == API.LLVMOrcSymbolLookupFlagsRequiredSymbol
+                name = LLVMSymbol(lookup.Name)
+                ptr = Libdl.dlsym(handle, name; throw_error=false)
+
+                if ptr !== C_NULL
+                    LLVM.retain(name)
+                    address = API.LLVMOrcJITTargetAddress(
+                        reinterpret(UInt, ptr))
+                    flags = API.LLVMJITSymbolFlags(
+                        API.LLVMJITSymbolGenericFlagsCallable, 0)
+                    symbol = API.LLVMJITEvaluatedSymbol(address, flags)
+                    push!(symbols, API.LLVMJITCSymbolMapPair(name, symbol))
+                end
+            else
+                @warn "Unkown" lookup.LookupFlags
+            end
+        end
+        mu = absolute_symbols(symbols)
+        define(JD, mu)
+        # TODO: API.LLVMErrorSuccess is not a LLVMErrorRef
+        return reinterpret(API.LLVMErrorRef, API.LLVMErrorSuccess)
+    end
+    return LLVM.CustomDefinitionGenerator(libdl_definitions)
+end
 
 function lookup_dylib(es::ExecutionSession, name)
     ref = API.LLVMOrcExecutionSessionGetJITDylibByName(es, name)
diff --git a/test/Project.toml b/test/Project.toml
index 6dd5450d..19351b9e 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,5 +1,6 @@
 [deps]
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 LLVMExtra_jll = "dad2f222-ce93-54a1-a47d-0025e8a3acab"
+NUMA_jll = "7f51dc2b-bb24-59f8-b771-bb1490e4195d"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
diff --git a/test/orcv2.jl b/test/orcv2.jl
index df0a51c4..5bff2ff2 100644
--- a/test/orcv2.jl
+++ b/test/orcv2.jl
@@ -302,4 +302,21 @@ end
     end
 end
 
+import NUMA_jll
+
+@testset "CustomDefinitionGenerator" begin
+    @dispose lljit=LLJIT() begin
+        if NUMA_jll.is_available()
+            @test_throws ErrorException lookup(lljit, "numa_available")
+
+            dg = LLVM.DynamicLibDefinitionGenerator(NUMA_jll.libnuma)
+            jd = JITDylib(lljit)
+            LLVM.add!(jd, dg)
+
+            addr = lookup(lljit, "numa_available")
+            @test addr !== C_NULL
+        end
+    end
+end
+
 end